A Fuel tank in conventional use has been made of metal; from the vehicle weight reduction, corrosion resistance and processability (into desired forms and shapes) points of view, however, thermoplastic resin-based ones have been proposed. Such thermoplastic fuel tanks which are currently in use consists of a polyolefin resin layer and an ethylene/vinyl alcohol [EVOH] resin-based barrier layer as produced by multilayer blow molding. For multilayer blow molding, however, an apparatus equipped with a mold for molding a fuel tank as a whole is required and, therefore, there arise various problems, namely high equipment cost, difficulty in adjusting the tank inner layer wall thickness, low design freedom, and lengthy molding cycle, among others. Further, since the EVOH resin is not satisfactory in gasoline resistance, it cannot be used as the innermost layer, so that problems arise: for example, the laminate structure may become complicated or there may appear a blow molding joint site where there is no EVOH resin layer.
As a thermoplastic resin-based fuel tank improved in low fuel permeability and/or flexibility, the following ones have been proposed, among others:
A Fuel tank molded from surface-fluorinated resin particles obtained by subjecting olefinic resin particles to surface fluorination treatment (cf. e.g. Patent Document 1: Japanese Kokai Publication 2005-170167); and
A Fuel tank comprising a permeation preventing layer made of an inorganic substance or a thermoplastic resin with an inorganic substance dispersed therein and a thermoplastic resin layer (cf. e.g. Patent Document 2: Japanese Kokai Publication 2002-144891).
However, even these methods cannot yet bring about necessary improvements; thus, a fuel tank more inexpensive and more improved in performance characteristics is demanded.
From such viewpoints, a method of molding a fuel tank which comprises joining together a plurality of constituent members molded in advance. As such a fuel tank, the following have been proposed, among others:
A fuel tank made of a resin composition resulting from blending of a polyoxymethylene resin and a carboxylic acid group or like group-containing olefin copolymer in a specific proportion (cf. e.g. Patent Document 3: Japanese Kokai Publication 2005-7943);
A fuel tank produced by a method comprising molding a pair of moldings made of a sheet-shaped laminate consisting of an internal layer, a permeation-preventing film or membrane and an outside layer and fusion bonding the pair of moldings together at the peripheries thereof (cf. e.g. Patent Document 4: Japanese Kokai Publication H05-16938);
A fuel tank produced by a method comprising joining an injection molded upper and lower moldings together by fusion bonding at the each split-opening peripheral edges and providing the thus-obtained substrate layer with a synthetic resin barrier layer integrally on the tank inside surface of the substrate layer by injection molding or injection compression molding (cf. e.g. Patent Document 5: Japanese Kokai Publication 2004-98886);
An automotive fuel tank formed of a thermoplastic synthetic resin-based inner resin layer and an outside resin layer which are produced by a method comprising joining an upper tank portion and a lower tank portion individually molded separately at the opening peripheries and coating the whole outer surface of the thus-formed inside resin layer integrally with an outer surface resin layer (cf. e.g. Patent Document 6: Japanese Kokai Publication 2006-160093); and
A fuel tank produced by a method comprising molding a plurality of plastic sheets respectively by vacuum forming and overlaying the peripheral seal regions of the respective moldings obtained with one another, followed by sealing by fusion bonding (cf. e.g. Patent Document 7: Japanese Kohyo Publication 2006-513062).
However, those fuel tanks are not yet satisfactory with respect to such performance characteristics as low fuel permeability and gasoline resistance.
Such conventional art fuel tanks, irrespective of the method of molding thereof, are insufficient in low fuel permeability, in particular poor in low fuel permeability against bio-fuels in current use and also insufficient in chemical resistance.